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A ROLE FOR SUCROSE SYNTHASE IN STARCH SYNTHESIS IN SWEET POTATO

蔗糖合成酶在甘薯淀粉合成中的作用

基本信息

批准号：
07456010
负责人：
SAITOU Kazuyuki
金额：
$ 5.12万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

In plants, sucrose is an energy and carbohydrate source. Sucrose is synthesized in photosynthetically sctive tissues and transported to other plant organs where it is used after cleavage to monosaccharides or derivatives. Sucrose synthase (SUS) is one of the enzymes involved in sucrose breakdown. To understand the molecular mechanisms in sugar distribution and metabolism of sweet potato, we have isolated a cDNA (1,191 bp) encoding SUS of sweet potato (IBSUS). The deduced amino acid of IBSUS was most closely related (91% homology) to potato SUS.Less homology (75%) was found to monocotyledonous sequences (rice and maize). The published Arabidopsis SUS sequence unexpectedly showed an even lower homology value of 69%. The activity of SUS in roots of sweet potato increased during development of tuberous roots. The enhancement of the enzymatic activity was accompanied by an increase in starch content. The activity of SUS in the tuberous roots was higher than that in the other tissues, namely, leaf blades, petioles, stems and fibrous roots. The enzymatic activity was not detectable in the leaf blade. Expression of the gene encoding SUS in different tissues of sweet potato was assessed by northem bolt hybridization. A signal of the SUS mRNA with a size of approximately 2.4 kbp was found in petioles, stems, fibrous roots and tuberous roots. The gene was most abundantly expressed in tuberous roots. Lower expression levels were found in petioles and stems, whereas no expression could be detected in leaf blades. The gene encoding SUS was strongly inducible by sucrose at the RNA level.

在植物中，蔗糖是能量和碳水化合物的来源。蔗糖在光合作用敏感组织中合成，并运输到其他植物器官，在那里分解成单糖或衍生物后使用。蔗糖合成酶（Sucrose synthase，SUS）是参与蔗糖分解的酶之一。为了解甘薯糖分布和代谢的分子机制，我们克隆了甘薯糖代谢系统基因（SUS of sweet potato，IBSUS）的cDNA（1，191 bp）。IBSUS的氨基酸序列与马铃薯SUS的同源性最高（91%），与单子叶植物（水稻和玉米）的同源性最低（75%）。公开的拟南芥SUS序列出乎意料地显示出69%的甚至更低的同源性值。甘薯块根中SUS活性随块根发育而增强。酶活性的增强伴随着淀粉含量的增加。在块根中SUS活性高于叶片、叶柄、茎和须根。在叶片中未检测到酶活性。利用Northem Bolt杂交技术检测了GUS基因在甘薯不同组织中的表达。在叶柄、茎、须根和块根中发现了一个大小约为2.4kbp的SUS mRNA信号。该基因在块根中表达量最高。在叶柄和茎中的表达量较低，而在叶片中没有表达。编码SUS的基因在RNA水平上被蔗糖强烈诱导。